1. Technical Field
The present invention relates generally to a method for forming images using photoimagible compositions and to substrates bearing an image prepared by such method and, specifically, to a dual component cross-linking system for producing positive-acting photoimagible epoxy resin formulations of the type useful as photoresists.
2. Description of the Related Art
The preparation of images by photopolymerization is well known. A photopolymerizable composition is applied as a coating to a substrate, which may be a resinous laminate bearing a metal on its surface. The coating is irradiated through a negative or other mask, and the unexposed (unpolymerized) portions of the coating are removed by means of a suitable solvent. The substrate may then be etched, removing only those parts of the metal surface which do not bear the photopolymerized coatings. Such image forming techniques are used, for example, in the manufacture of printed circuits.
Where epoxy resins have been utilized as the polymerizable component, they have generally been negative working, whereby the material which is exposed to irradiation cross-links and subsequently becomes unaffected by the developing solvent. Materials that cross-link upon exposure and remain through all of the developing steps are referred to as "negative-working." An example of such a negative working epoxy-photoresist system is shown, for example, in U.S. Pat. No. 4,439,517, issued Mar. 27, 1984, to Irving, entitled "Process For The Formation of Images With Epoxide Resin."
The present invention has as its object to provide a positive-acting, photoimagible epoxy resin system. Such a resin system would be of advantage whenever the application required a photoimagible polymer which would cure in the unexposed areas; for instance where it is impossible or impractical to provide light to the areas to be cured.